The present invention relates generally to a filter element for filtering of liquids, and more particularly to a coiled filter element for the filtration of liquids.
It is already known from U.S. Pat. No. 3,739,916 to provide a coiled filter element by convoluting a strip of filter material which is first folded to a substantially V-shaped configuration so as to have two superimposed strip portions, both of which define with one another a V-shaped pocket or cross section. When these strip portions are convoluted they form two spirally intercalated internal filter chambers one of which is open in the region where the free edges of the strip portions are located, and the other of which is open in the region where the unitary edges of the strip portions are located. Such a filter element, which may be made of conventional filter paper or the like, has been found to be highly advantageous, but has also been found to have one significant disadvantage which requires correction. In particular, it is found that when liquid to be filtered and containing contaminant particles, enters into the open side of the V-shaped cross section defined between the two strip portions, pressure variations which take place in the region where the unitary edges of the two strip portions are located, tend to force contaminant particles through the material of the strip together with the liquid which is being filtered. This of course disadvantageously influences the degree of effectiveness of the filter element.